Manufacture of ethyl alcohol from sulphite residual liquor



Oct. 14, 1947.

G. H. TOMLINSON MANUFACTURE 0F ETHYL ALCOHOL FROM SULPHITE RESIDUAL LIQUOR EEE@ siam mm, Lmmbm.

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2 Sheets-Sheet 1 um 23k@ LNB@ www mmuwnmbgm QSQ n Y n o Y m m m mm m m A Patented Oct. 14, 1947 MANUFACTURE OF ETHYL ALCOHOL FROM SULPHITE RESIDUAL LIQUOR George H. Tomlinson, Montreal, Quebec, Canada, assigner to Howard Smith Paper Mills Limited, Montreal, Quebec, Canada. a company Application May 20, 1943, Serial No. 487,698

S Claims.

The present invention relates in general to improvements in the manufacture of pulp by the digestion of cellulosic fibrous material in a relatively pure magnesium base sulphite cooking liqucr, and more particularly, to an improved cyclic system for recovering chemicals and heat from the residual pulp liquor in a process of this charn acter.

The general object of my invention is the provision of an improved cyclic process of treating the residual pulp liquor in a system of the character described to recover the base chemicals of magnesium and sulphur in a form permitting their economic reuse in the pulping process, and heat in economic quantities, as well as an economic utilization of the fermentable sugars in the residual liquor for the production of ethyl alcohol, while completely eliminating any disposable problem.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Figs. 1 and 1A collectively constitute a flow diagram of a cyclic sulphite pulp residual liquor recovery system embodying my invention.

It is well known that sulphite pulp residual cooking liquors contain fermentable sugars formed during the digestion or cooking operation which can be fermented and the ethyl alcohol formed separated by distillation and rectilication. The manufacture of ethyl alcohol from sulphite waste liquor however has been found to be a marginal operation from an economic standpoint in most countries due to its low alcohol yield in comparison to alcohol manufactured from molasses and grains and the high initial equipment investment required. In general such processes use the successive steps of draining the waste liquor from the pulp to avoid dilution of the liquor, aeration of the liquor to eliminate sulphur dioxide. addition of slaked lime and/or calcium carbonate to neutralize the liquor to a pH value satisfactory for fermentation, addition of nutrients to aid fermentation, fermentation by a suitable yeast, and finally concentration and rectification of the ethyl alcohol.

With such systems yields of ethyl alcohol based on the liquor may range from 0.5 to 1.4% by volume. about 1% being the average obtained under favorable conditions as, for example. when only that portion of the liquor is used whim 1. an be drained from the digestor or blow pit et maximum concentration, this amounting tu about or '70% of the total liquor. In the absence of an expensive washing plant much more than this cannot be recovered without excessive dilution, the latter necessitating a more expensive distillery. The average yield based on the pulp is about 10 gallons per ton, while the theoretical maximum yield based on the polysaccharides in the wood, is about 47 gallons per ton of pulp. The only way heretofore considered possible to obtain any large increase in the ultimate yield of alcohol from sulphite waste liquors has been through modification of the cooking operation to produce waste liquor of higher sugar content by using a cooking liquor of low lime content and cooking until the maximum sugar yield is reached. The more favorable conditions for sugar production however also result in greater attack on the cellulose, with a consequent decrease in pulp strength and yield.

Even the larger yield of alcohol per ton of pulp so obtained is not competitive with alcohol produced from such cheap sources of sugar as blackstrap molasses, as the yield with the latter is six to ten times as great for the same amount of equipment. The described manufacture of ethyl alcohol from sulphite liquor modies, but does not eliminate the problem of stream pollution, so that is not a factor beneficial to such development. The result has been that only in countries where production has been subsidized or protected from competition from alcohol from other sources has it been practical to carry on the manufacture of ethyl alcohol from waste sulphite liquor.

Sulphite residual liquor as drained from the digesters normally contains from lil-14% solids. Concentration of this liquor before fermentation and distillation is considered impractical because the increased yield of alcohol would be more than offset by the high cost of the evaporating equipment and of the steam required for evaporation. Furthermore, concentration of a calcium base waste liquor has been found to be impractical because of the time and expense of maintaining such evaporating equipment clear of the calcium sulphate scale which tends to form on any heating surface contacted by such liquor.

In accordance with my invention, the manufacture of ethyl alcohol from sulphite residual awaits cooking liquor is made economical and commercially desirable by incorporating such an operation in and as a part of a cyclic process for the recovery of chemicals and heat from a relatively pure magnesium base sulphite residual cooking liquor of the type disclosed in my prior Patents 2,238,456 and 2,285,876 and my pending application Serial No. 387,474, led April 8, 1941.

In such cyclic systems a cooking liquor consisting of a relatively pure acid sulphite compound of magnesium, i. e. magnesium bisulphite, with an excess of sulphur dioxide. is supplied to a digester Il) from a cooking acid tank II. The digester I is equipped for indirect heating. permitting the Baume of the residual liquor following cooking to be maintained at a higher value than would be possible if direct steaming were employed. A more economical evaporation of the liquor to the desired concentration is thus made possible.

When the cooking operation is completed the contents of the digester may be discharged into a biow pit I2 from which gases are vented and the pulp and liquor pumped to suitable pulp wasning equipment, such as rotary vacuum filters I3 and I4 arranged in series. Wash water from a hot Water tank I5 is delivered to the pulp washer I4 as indicated and the nitrate discharged into a tank I6. from which a portion is delivered to the pulp washer I3 to serve as wash liquor therein. The filtrate from the second washer Il is also employed to insure the correct consistency of the pulp going to that washer by returning a portion of the filtrate to the stock box of the washer M A further advantageous use of this filtrate is as a basis for the magnesia suspension employed in the absorption towers. even though this will result in the circulation of a small amount of inert solids in solution in the total system, as the nitrate thus forms the basis of subsequent fresh cooking liquor. The filtrate from the first washer I3 is sent to an acid liquor tank I1 from which a portion is returned to the stock box of the washer I3, and another portion to the blow pit l2 to increase the fluidity of the pulp and thus facilitate its delivery to the pulp washers. Substantially all of the liquor and washer filtrate is thus maintained in the system, the only loss being that carried out by the pulp leaving the second Washer I4 for subsequent treatment in the knotters, riillers, bleachers and dryers.

The residual liquor in the tank I1 will have essentially the same solid content asthat leaving theuigetei-wraieamcr @advantageously sa iizifl'sithfviaififders asserisce-r essorage tatieg 1a 'einen' reeivestiiei heating ss'fgciiv ertedih thechemicafliverypfrnaci afteraj' major portion ofthe solid chemicalsiira'i'fe lbeen' separated therefrom, and prior to their passage through absorption towers. The spraying of the liquor into intimate contact with the hot gases effects the liberation of free sulphur dioxide in the liquor which upon its liberation is carried with the heating gases for recovery in the subsequent g5 absorption towers. It also results in the recovery of most of the small amount of solid chemicals present in the gases coming to the scrubber, and the magnesium oxide so recovered partly neutralizes this liquor. Some evaporation of the acid waste liquor also results, reducing the amount of concentration to be done in the evaporators and thus saving steam.

The partly neutralized and partly concentrated residual liquor is then pumped from the scrubber and the neutralization is then completed by the controlled addition of magnesium oxide to a mixing tank I9 and delivery to the neutral liquor tank 2D. The neutralization is either completely or very largely accomplished by the use of recovered ash. but as indicated, if magnesia is used as make-up to the system, the fresh magnesia may be introduced at this point. both of the reagents being readily soluble in the acid liquor. The residual liquor before neutralization is highly corrosive, having a pH of 2.5 to 3.0, and unless neutralization is eeeted the equipment handling the liquor must necessarily be made of relatively expensive corrosion-resistant alloy. Neutralization of the acid residual liquor prior to the delivery of the liquor to a multiple effect evaporator is also important in that it effects the combination of any remaining free SO2, thus preventing its liberation in the evaporator, a condition which would adversely affect the vacuum in the evaporators. The optimum pH range for yeast activity is between 5.5 and 6.5, and since the liquor during its passage through the evaporator may change slightly, the neutralization of the liquor is preferably carried into a slightly higher pH range as, for example, pH? or more, prior to its evaporation, Following its evaporation and immediately prior to its fermentation, the pH is then adjusted, if necessary, by adding H2804 or the like.

The neutralized and partly concentrated residual liquor is allowed to settle in the tank 20 until `clear and the clear liquor thus separated is then further concentrated under vacuum to a concentration range suitable for fermentation. With a suitable strain of yeast, preferably one grown in waste sulphite liquor and therefore acclimatized to the same, I have found that the alcohol yield increases approximately in proportion to the increase in the solid content oi' the liquor until concentration of about 35% total solids is reached. When the concentration is carried beyond this value, however, the alcohol yield begins to diminish quite rapidly.

In my preferred system illustrated, the liquor is evaporated to the desired concentration by passing the neutralized liquor from the tank 2li to an intermediate stage of a multiple-effect evaporator, shown as a five-stage evaporator, the evaporator stages being numbered 1 to 5, in the first stage of which the liquor is heated by exhaust steam from a back pressure turbine 2|. The steam condensate from the rst evaporator heating effect is advantageously used as part of the boiler feed water supply, the condensateffom effect itpas'ses1i siccessiveiy'through the fourth and fifth effects, leaving the fifth effect with a temperature of about F. and a concentration between 28% and 35% total solids. The liquor on leaving the fifth effect is therefore in a suitable condition for fermentation and distillation purposes inasmuch as it will have a pH value such that this will require only some minor adjustment and will have a concentration of from two to three times its original value and a temperature approaching that required for effective fermentation.

As indicated in Figs. 1 and 1A, the concentrated liquor is delivered to a receiving tank 30 from which it is delivered by a pump 3l through a cooler 32, in which the temperature is reduced to about 90 F., to the fermentation vats 33. 'I'he fermentation is carried out in the usual way with a suitable distilling yeast, the necessary nutrients being supplied for the support of the yeast. The fermentation requires from one to three days for completion, the resulting beer being delivered to a storage tank 3l. The beer will normally have an ethyl alcohol content of from 2% to 3% by volume, a value two or three times greater than can be obtained from the original unconcentrated sulphite residual liquor. From the tank 34 the beer is delivered to a beer still for the removal of the alcohol and other volatile constituents. The described preparation of the beer renders it suitable for distillation in a continuous type column-still without clogging such apparatus. A conventional continuous beer still is indicated having a feed tank l5, a feed heater 3B, a column-still 31 with a steam inlet 38, a condenser 39, and a storage tank 40 for the distillate. The exhausted liquor is discharged from the bottom of the still 31 to a receiving tank 4I at a temperature of approximately 212 F. The distillate is delivered to a suitable rectifying still for the elimination of impurities and substantially all of the remaining water.

With the described withdrawal of the residual liquor to the alcohol fermentation and distillation section of the system at a concentration which materially reduces the volume to be handled, and yet at a concentration suitable for fermentation, i. e. not over about three times the initial solid concentration of the liquor, the required capacity of the fermenting vats and distillation equipment is reduced in direct proportion to the degree of concentration. The amount of distillation steam required is also substantially reduced.

The residual liquor from the alcohol distillation system is advantageously adjusted in pH value by the addition of magnesium oxide to avoid any corrosive effect and returned to the evaporators, entering the second evaporating stage at a higher temperature (about 212 F.) than when leaving the fifth stage (120 FJ. A considerable part of the heat value of the steam used in the distillation operation is thus recovered. The liquor is further concentrated in the second and first evaporating stages, leaving the latter at a concentration of between 45 and 70% solids. The concentrated liquor is discharged to the concentrated liquor storage tank l5, from which it is withdrawn as required by the recovery furnace unit 50. The liquor is then in a condition similar to the liquor supplied to the recovery furnace as disclosed in my said prior patents and pending application except for the loss of the heat value of the sugars fermented and recovered as alcohol. About to 15% of the organic matter contained in the original waste liquor solids is utilized in the described method of making ethyl alcohol. The higher commercial value of the alcohol greatly exceeds the combustible value of these sugars, permitting the use of an equivalent amount of auxiliary fuel in the recovery furnace, if desired.

By way of example, and not of limitation, in one experimental run of the process, the residual liquor when sampled at the digester concentration contained 10.5% waste sulphite liquor solids. The recovered liquor was neutralized with MgO to a pH of 7.5 and the clear liquor evaporated to a specific gravity of 1.203 when it then contained 35.34% total solids. 'I'he concentrated liquor was cooled to 93 F., its pH value adjusted to 5.74 and nutrients were added, following which it was fermented with a yeast acclimatized to waste sulphite liquor. Fermentation was complete in 24 hours and the beer then contained 2.64% alcohol by volume. After distillation of the alcohol, the pH of the liquor was 5.54, and it contained 33.5% solids. 'Ihe pH value was then adjusted by MgO additions to 7.5 and the liquor evaporated to a final concentration of 58.5% solids, a concentration suitable for self-sustaining combustion thereof in the recovery furnace.

Magnesium sulphite formed by free SO2 combining with MgO in the tank 20 and settling out therein due to its low solubility may be advantageously collected therefrom and mixed with the highly concentrated liquor before delivery into the recovery furnace. Any sulphur loss can thus be avoided and the amount of magnesium sulphite entering the evaporator and fermentation vats considerably reduced.

The concentrated liquor from the storage tank 45 is atomized into a finely divided spray in the chemical recovery unit l0 and burned therein in suspension under self -sustaining combustion conditions to yield a dry ash consisting mainly of caustic magnesium oxide (MgO) and heating gases including SO2 which are subsequently utilized to produce more than enough steam to satisfy the requirements of the system. The construction and operation of the recovery unit Il is similar to that disclosed and claimed in a copending application of Leslie S. Wilcoxson, Serial No. 347,944, filed July 27, 1940.

The high cost of chemicals involved in a pulping process employing a relatively pure magnesium base cooking liquor requires a cyclic recovery process having a high eiliciency of recovery of the heat and chemical values of the residual liquor to be economic. The chemicals, sulphur and magnesium oxide, must also be recovered in a form which permits their economic reuse in the pulping process and the heat values in the liquor must be recovered in economic quantities. This requires that the magnesium compounds recovered have a high percentage of magnesia (MgO) of a high reactivity and free from carbon, and that the sulphur content be recovered in the form of sulphur dioxide in order that the chemicals may be readily recombined to form a sulphited magnesia. The burning of the combustible organic constituents of concentrated liquor will generate products of combustion having an extremely low sulphur dioxide content, i. e. less than 1%. Any attempt to recover the sulphur dioxide from the gases under such conditions is unusual because its recovery can only be effected in the presence of an extremely reactive reagent. An overheated or dead-burned" magnesia would consequently be useless. In fact, the magnesia should preferably be more reactive than the best grades of commercial caustic magnesia to eil'ect the desired amount of sulphur dioxide recovery under such conditions.

Magnesia is commercially produced by the calcination of magnesium compounds, such as magnesite, by coal or carbon mixed with the material. It is known that the reactive character of the resultant magnesia depends upon the amount of carbon present in the mixture; and it is generally considered that for the production of caustic magnesia, the amount of coal or carbon used should not exceed about 20% of the weight of the magnesite. For the commercial production of dead-burned magnesio.. it is the customary practice to mix from 30% to 50% coal with the magnesite.

In one representative analysis of the concentrated liquor, the carbon was 25.04% and the ash (i. e. the magnesium compounds) 6.87%. Accordingly, if such liquor were evaporated to dryness before being introduced into a furnace and the dried solids then burned, the material would then include an amount of carbon over ten times the amount of carbon required for producing dead-burned magnesia. Complete combustion of the organic constituents of the residual liquor is highly desirable. both in the interests of thermal eiiiciency and to obtain an ash as free from impurities as possible in order to minimize the subsequent filtering operation.

In accordance with my recovery process. pulp residual liquor of the character described can be treated to obtain an ash containing a high percentage of magnesia of a high reactivity and free from carbon while maintaining desirable combustion conditions in the recovery furnace. It has been found that recovery furnace conditions suitable for obtaining certain of these characteristics are not suitable for obtaining others. For example, it is important that any magnesium compounds in the form of magnesium sulphate be reduced to magnesium oxide while in the furnace as the sulphate is of no value in the cooking liquor and would form a dead load of chemical circulating through the system. The greatest reduction of the sulphate will occur when a high temperature reducing atmosphere is maintained in the furnace. However, high temperature conw ditions are not suitable for obtaining the highly reactive caustic magnesia desired, nor is a highly reducing atmosphere suitable for a complete combustion of the combustible portions of the liquor. Complete combustion of the combustible matter is favored by the use of a substantial amount of excess air in the furnace, but such conditions tend to increase the percentage of sulphur dioxide (SO2) converted into sulphur trioxide (S03) this reaction being accelerated in the temperature range (1000l200 F.). While any sulphur trioxide in the heating gases can be recovered in the absorption towers, it would combine with the magnesia in the slurry to form magnesium sulphate and add to the dead load of circulating chemicals. The production of caustic magnesia of the desired reactivity, i. e. a mean reactivity at least greater than 1.5 on an arbitrary scale which has been devised, on which ordinary commercial caustic magnesia has a mean reactivity of 2.1, requires careful control of the temperature and atmosphere conditions, velocity of gas ow in the furnace, and size of the ash particles. It has been found that furnace temperatures in the range of 18002400 F., and preferably 2i002300 F., are most desirable with a rapid passage of the ash particles through the furnace sections having such temperatures, the permissible time of exposure decreasing as the temperature increases. If the exposure at these ternperatures is more than momentary, the reactivity of the magnesia diminishes and even dead burning is likely to occur.

To permit the efilcient recovery of magnesium and sulphur in a form permitting their economic reuse in the cyclic system, introduction of the chemicals into the furnace in a concentrated liquor of the character described and maintenance of predetermined temperatures. atmospheres and gas velocities in different portions of the unit are of prime importance. A long dame combustion of the combustible constituents of the residual liquor under a reducing atmosphere while in intimate contact with the magnesium constituents is considered desirable to avoid excessive furnace temperatures and possible deadburning of the magnesia. For this purpose the total amount of combustion air supplied to the furnace is only slightly in excess of the theoretical combustion requirements and that air is supplied to the furnace at widely spaced points along the flow path in predetermined proportions. A total combustion air approximately of the theoretical requirements has been found suitable. for example.

The ash produced will be mainly in the form of light cenospheres and flakes having a density of from three to eight lbs/cu. ft., the density increasing as the reactivity decreases. The percentage of caustic magnesium oxide in the ash will depend upon the elciency of reduction. Normally the caustic magnesium oxide content will be at least 70%, with the remainder mainly magnesium sulphate and carbonate. Very small percentages of inorganic impurities will also be present, these varying with the wood used.

The steam boiler 5i is characterized by its simplicity of construction and ease in which its heating surface can be kept absolutely clean of ash. The furnace temperatures maintained are below the fusion temperature of the ash, and the tubes and baffles of the boiler are so arranged that any of the dry ash depositing thereon can be readily removed. The ability to maintain the boiler heating surface absolutely clean minimizes the draft loss and permits the use of high gas velocities, such as 50 feet per second, for example, consistent with the economical utilization of induced draft fan power requirements and consequently results in highly efficient heat transfer conditions.

On leaving the boiler, the heating gases pass upwardly, through the tubes of an air heater 52 with the air to be preheated flowing downwardly around the tubes under the action of a forced draft fan 53. The gases then ow in parallel through the dust collecting cyclones 54 forming the separating apparatus. Most of the chemical ash in suspension is separated at this point and collected in hoppers at the bottom of the cyclones. The gases then pass out through the induced draft fan 55 to the spray tower or scrubber i3, in which they successively contact descending sprays of residual liquor delivered from the tank I1. The gases then flow to the absorption towers 51 and 5B. The liquor is pumped from the bottom of the spray tower to the mixing tank I9 and neutralizing tank 20.

The ash produced by the spray burning of the liquor and separated in the cyclone separators 54 is delivered to an ash storage tank 59. Most of the remaining ash in the gases is removed during the passage of the gases through the scrubber I8. as has been described. On leaving the scrubber the gases are delivered to the serially connected absorption towers 51 and il for the recovery of the sulphur content of the gases. In the sulphur absorption towers, the gases are subjected to contact with a slurry consisting mainly of magnesia in suspension formed by mixing the ash from the tank 59 with the filtrate from the second pulp washer I4 in a tank 00. The slurry is fed into the top of each absorption tower and passes downwardly over wooden slats therein in counter-current relation to the relatively low temperature ascending gas. During its passage through the tower the magnesla in suspension combines with the sulphur dioxide content of the gases and forms a solution of sulphited magnesium. Any sulphur trioxide present in the towers will combine to form magnesium sulphate in the resulting liquor which relation while forming the A inert sulphate, retains the chemicals in the system for subsequent reduction and reuse. By the foregoing operations the gases passing from the upper end of the absorption tower B to the stack have had both their solid magnesium oxide and gaseous sulphur compounds efficiently removed and are consequently innocuous.

In order to have and maintain the greatest recovery efficiency in the absorption towers, a balance is required between the amount of magnesium oxide in the slurry and the amount oi sulphur dioxide in the gases. The accumulation of calcium impurities in the system is controlled to cause the sulphited calcium to remain ln suspension and the magnesium to go into solution as sulphite and bisulphite. I'he slurry fed to the towers is preferably a liquor of high alkalinity, i. e. a liquor having a pH value of about 9.5. but as an increasing amount of sulphur dioxide is combined. the pH value falls, first gradually and then rapidly. The pH value of the liquor leaving the absorption tower 51 is preferably maintained within the pH range of 4.0-7.0, whereby any calcium sulphite formed from calcium impurities in the residual liquor will be relatively insoluble and remain in suspension and the sulphited magnesium formed will be highly soluble. The amount of slurry serially supplied to the absorption towers 58 and 51 is automatically controlled in response to variations in the percentage of SO2 in the gases passing to the absorption towers, by means nf an automatic S01 analyzer 62 and a remote control valve 63. The alkaline liquor leaving the second absorption tower 51 is passed through a liquor cooler B4 in which its temperature is reduced to facilitate the subsequent absorption of SO2 from the sulphur burners 65. The operation of the valve B3 in response to the SO: analyzer is checked by having a pT-l. control 6B at the discharge side of the cooler 6I act on the valve 63. preferably between the operating intervals of the SO2 analyzer. An SO2 recorder 61 is also employed.

The necessity for clean cooking liquor, in view oi the possibility of some solids being present in the washer filtrate and the collection of solids in the form of unburned carbon from the gases in the absorption tower, is provided for by filtering the liquor in a suitable filter B8. Bv having the filter subsequent to the pH control operation. the calcium compounds in suspension in the liquor can be removed along with any carbon or other solid particles. The magnesium bisulphite liquor is fortified to the desired sulphur dioxide concentration by bringing sulphur dioxide, generated by the sulphur burners 65 and cooled in the gas cooler 69, into contact with the liquor while passing through a gas absorption system 1D. The fortified liquor is then delivered to a tank 1| where it is mixed with relief gases from the digester i0 before being delivered to the cooking acid storage tank Il.

With my improved cyclic system for the recovery of chemicals and heat from relatively pure magnesium base sulphite residual liquor, the a1- .cohol production costs are substantially decreased to approximately one-third cf the cost of alcohol when made as an isolated operation with a sodium or calcium base sulphite residual liquor,

In the present system, the alcohol costs are represented by the B. t. u. value of the fermented sugars, part of the cost of steam for distillation, interest and amortization of a substantially smaller amount of fermenting and distilling equipment, and a small amount of additional labor. The steam production of a modern liquor recovery unit is more than sufficient to cover the process and heating requirements of the usual sulphite mill and chemical recovery system. leaving a surplus available for sale in a limited market. The incorporation of the alcohol section in the system and consequent lower recovery of heat values with the combined system is more than offset by the value of the alcohol produced. No material change occurs in the disposal problem, all of the constituents of the residual liquor being recovered or completely eliminated thus avoiding any question of stream pollution.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will understand that changes may be made without departing from the spirit of the invention covered by my claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

l. The method of treating the residual liquor resulting from the digestion of cellulosc fibrous material in a relatively pure magnesium base sulphite cooking liquor which comprises neutralizing the residual liquor by the addition of caustic magnesia to a pH value suitable for sugar fermentation, concentrating the neutralized liquor to a concentration above 20% solids, fermenting the fermentable sugars in the concentrated liquor to produce beer, distilling the beer and rectifying the ethyl alcohol obtained therefrom, introducing the liquor residue from the distilling operation into a high temperature furnace chamber, burning the combustible constituents of the liquor so introduced therein while maintaining a furnace chamber temperature below the fusion temperature of the non-combustible constituents of the liquor to yield an ash residue containing caustic magnesia. removing substantially all of the ash residue produced from the combustion zone in such a brief period of time that the exposure of the ash residue within the Acombustion zone is insuflicient to effect deadburning of the magnesia in the ash residue, and treating the ash residue removed to form fresh magnesium base sulphite cooking liquor.

2. The method of treating the residual liquor resulting from the digestion of cellulosc fibrous material in a relatively pure magnesium base sulphite cooking liquor which comprises neutralizing the residual liquor by the addition of caustic magnesia to a pH value suitable for sugar fermentation, concentrating the neutralized liquor to a concentration in the range of approximately 28-35% solids fermenting the fermentable sugars in the concentrated liquor to produce a beer, distilling ethyl alcohol from the beer, returning the liquor residue from the distillng operation for further concentration to a concentration within the range of 45-70% solids, spraying the concentrated liquor into a high temperature furnace chamber. burning the combustible constituents of the liquor so introduced therein to yield an ash residue containing caustic magnesia. and treating the ash residue l1 to form fresh magnesium base sulphite cooking liquor.

3. 'I'he method of treating the residual liquor resulting from the digestion of cellulosic fibrous material in a relatively pure magnesium base sulphite cooking liquor which comprises neutralizing the residual liquor by the addition of caustic magnesia to a pH value suitable for sugar fermentation, concentrating the neutralized liquor to a concentration in the range of approximately 28-35% solids fermenting the fermentable sugars in the concentrated liquor to produce a beer. distilling ethyl alcohol from the beer. returning the liquor residue from the distilling operation for further concentration to a concentration within the range of i5-70% solids, spraying the concentrated liquor into a high temperature furnace chamber, burning the combustible constituents of the liquor so introduced therein while maintaining a furnace chamber temperature below the fusion temperature of the non-combustible constituents of the liquor to yield an ash residue containing a relatively high proportion of caustic magnesia, removing substantially all of the ash residue produced from the combustion zone by flotation in the gaseous products of combustion in such a brief period of time that the exposure of the ash residue within the combustion zone is insuillcient to eifect dead-burning o! the magnesio. in the ash residue, and treating the ash residue removed to form fresh magnesium base sulphite cooking liquor.

4. The method of treating the residual liquor resulting from the digestion oi cellulosic ilbrous material in a relatively pure magnesium base sulphite cooking liquor which comprises partly concentrating the residual liquor by direct contact with gaseous products of combustion, neutralizing the partly concentrated residual liquor by the addition oficaustic mmesiafto a pH valuersuitable for sugar fermentation. concentrating the neutralized liquor to a concentration in the range of approximately 2li-35% solids, fermenting the fermentable sugars in the concentrated liquor to produce a beer, distilling ethyl alcohol from the beer, returning the liquor residue from the distilling operation for further concentration to a concentration within the range of 45'l0% solids. spraying the concentrated liquor into a high temperature furnace chamber, burning the combustible constituents oi the liquor so introduced therein to yield an ash residue containing caustic magnesia, contacting the gaseous products of combustion with the residual cooking liquor to partly concentrate the liquor, and treating the ash residue removed to form fresh magnesium base sulphite cooking liquor.

5. The method of treating the residual liquor resulting from the digestion of cellulosic fibrous material in a relatively pure magnesium base sulphite cooking liquor which comprises partly burning the combustible constituents oi the liquor so introduced therein While maintaining a furnace chamber temperature below the fusion temperature of the non-combustible constituents oi the liquor to yield an ash residue containing a relatively high proportion of caustic magnesia, removing substantially all of the ash residue produced from the combustion zone by flotation in the gaseous products of combustion in such a brief period of time that the exposure of the ash residue within the combustion zone is insuillcient to effect dead-burning of the magnesia in the ash residue, contacting the gaseous products of combustion with the residual cooking liquor to partly neutralize and concentrate the liquor, and treatlng the ash residue removed to form fresh magnesium base sulphite cooking liquor.

6. The method of treating the residual liquor resulting from the digestion of cellulosic fibrous material in a relatively pure magnesium base sulphite cooking liquor which comprises neutralizing the residual liquor by the addition of caustic magnesia, evaporatlng the neutralized liquor to a concentration in the range of 28-35% solids. fermenting the fermentable sugars in the concentrated liquor to produce a beer, distilling ethyl alcohol from the beer, returning the liquor residue from the distllling operation for further evaporation to a concentration within the range of 45- 70% solids, spraying the concentrated liquor into a high temperature furnace chamber, burning the combustible constituents of the liquor so introduced therein to produce gaseous products of combustion containing in suspension an ash resiconcentrating the residual liquor bydirect con- 1 tact with gaseous products of combustion. neu-` due containing caustic magnesio, passing the ash residue produced and the gaseous products of combustion through a steam generating zone, utilizing part of the steam generated for the evaporating operations and another part for the distllling operation, separating the ash residue from the gaseous products of combustion, and treating the ash residue removed to form fresh magnesium base sulphite cooking liquor.

7. The method of treating the residual liquor resulting from the digestion of cellulosic fibrous material in a relatively pure magnesium base sulphite cooking liquor which comprises neutralizing the residual liquor by the addition oi' caustic magnesia, evaporating the neutralized liquor to a concentration in the range of 28-35% solids by multiple eilect evaporation. fermenting the iermentable sugars in the concentrated liquor to produce a beer. distilling ethyl alcohol from the beer, returning the liquor residue from the distilling operation for further multiple eiIect evaporation to a concentration within the range of 45-70% solids, spraying the concentrated liquor into a high temperature furnace chamber burning the combustible constituents of the liquor so introduced therein to produce gaseous products of combustion containing in suspension an ash residue containing caustic magnesiappassing the ash residue produced and the gaseous products of combustion through. ai steam generating me, i

utilizing part-ei 'the steamgeneratedor the mu1- tipie eii'ectwevaporation'and another portion fthe" distilling operatiom separating utile-'ash residue from the gaseous products of combustion, and treating the ash residue separated to form fresh magnesium base sulphite cooking liquor.

8. The method of treating the residual liquor resulting from the digestion of cellulosic brous material in a relatively pure magnesium base sulphite cooking liquor which comprises neutralizing the residual liquor by the addition of caustic magnesia to a pH value above 6, evaporating the neutralized liquor to a concentration in the range oi 28-35% solids by multiple eect evaporation, adjusting the pH value to between 5.5 and 6.5, fermenting the fermentable sugars in the concentrated liquor with a yeast acclimatized to sulphite residual liquor to produce a beer, distilling ethyl alcohol from the beer, returning the liquor residue from the distilling operation for further multiple effect evaporation to a concentration within the range of 45-'70% solids, spraying the concentrated liquor into a high temperature furnace chamber, burning the combustible constituents of the liquor so introduced therein to produce gaseous products of combustion containing in suspension an ash residue containing caustic magnesia, passing the ash residue produced and the gaseous products of combustion through a steam generating zone, utilizing part of the steam generated for the multiple eiect evaporation and another part for the dlstilling and rectifying operations, separating the ash residue from the gaseous products of combustion, and treating the ash residue separated to form fresh magnesium base sulphite cooking liquor.

9. The method of treating the residual liquor resulting from the digestion of cellulosic ilbrous material in a relatively pure magnesium base sulphite cooking liquor which comprises neutralizing the residual liquor by the addition of caustic magnesia to a pH value above 6, evaporating the neutralized liquor to a concentration in the range of 28-35% solids by multiple effect evaporation, adjusting the pH value to between 5.5 and 6.5. fermenting the fermentable sugars in the concentrated liquor with a yeast acclimatized to sulphite residual liquor to produce a beer, distllling and rectifying ethyl alcohol from the beer, returning the liquor residue from the distilling operation for further multiple effect evaporation to a concentration within the range of i5-'10% solids, spraying the concentrated liquor into a high temperature furnace chamber, burning the combustible constituents of the liquor so introduced therein to produce gaseous products of combustion containing in suspension a dry unsintered ash residue having a relatively high proportion of caustic magnesia, passing the ash residue produced and the gaseous products of combustion through a steam generating zone, utilizing part of the steam generated for the multiple effect evaporation and another part for the distilling and rectifying operations, separating the ash residue from the gaseous products of combustion, and treating the ash residue removed to form fresh magnesium base sulphite cooking liquor.

GEORGE H. TOMLINSON.

RFEREN CES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,253,854 Marchand Jan, 15, 1918 2,285,876 Tomlinson June 9, 1942 2,238,456 Tomlinson Apr. l5, 1941 '757,352 Sanguineti Apr, 12, 1904 2,272,982 Owen Feb. 10, 1942 1,510,196 Romer Sept. 30, 1924 1,218,638 Fest Mar. 13, 1911 OTHER REFERENCES De Becze and Rosenblatt, "Continuous Fermentation, American Brewer, February 1943, pages 1l to 34. Pages 15-34 refer to alcohol.

Certicate of Correction Patent No. 2,429,143.

October 14, 1947.

GEORGE H. TOMLINSON It is hereby and that the said Letters the same may conform to certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column dlsposable read disposal; column l1, line 11, claim 3, after l, line 18, for the word solids insert a comma;

Signed and sealed this 6th day of January, A. D. 1948.

THOMAS F. MURPHY,

magnesia to a pH value above 6, evaporating the neutralized liquor to a concentration in the range oi 28-35% solids by multiple eect evaporation, adjusting the pH value to between 5.5 and 6.5, fermenting the fermentable sugars in the concentrated liquor with a yeast acclimatized to sulphite residual liquor to produce a beer, distilling ethyl alcohol from the beer, returning the liquor residue from the distilling operation for further multiple effect evaporation to a concentration within the range of 45-'70% solids, spraying the concentrated liquor into a high temperature furnace chamber, burning the combustible constituents of the liquor so introduced therein to produce gaseous products of combustion containing in suspension an ash residue containing caustic magnesia, passing the ash residue produced and the gaseous products of combustion through a steam generating zone, utilizing part of the steam generated for the multiple eiect evaporation and another part for the dlstilling and rectifying operations, separating the ash residue from the gaseous products of combustion, and treating the ash residue separated to form fresh magnesium base sulphite cooking liquor.

9. The method of treating the residual liquor resulting from the digestion of cellulosic ilbrous material in a relatively pure magnesium base sulphite cooking liquor which comprises neutralizing the residual liquor by the addition of caustic magnesia to a pH value above 6, evaporating the neutralized liquor to a concentration in the range of 28-35% solids by multiple effect evaporation, adjusting the pH value to between 5.5 and 6.5. fermenting the fermentable sugars in the concentrated liquor with a yeast acclimatized to sulphite residual liquor to produce a beer, distllling and rectifying ethyl alcohol from the beer, returning the liquor residue from the distilling operation for further multiple effect evaporation to a concentration within the range of i5-'10% solids, spraying the concentrated liquor into a high temperature furnace chamber, burning the combustible constituents of the liquor so introduced therein to produce gaseous products of combustion containing in suspension a dry unsintered ash residue having a relatively high proportion of caustic magnesia, passing the ash residue produced and the gaseous products of combustion through a steam generating zone, utilizing part of the steam generated for the multiple effect evaporation and another part for the distilling and rectifying operations, separating the ash residue from the gaseous products of combustion, and treating the ash residue removed to form fresh magnesium base sulphite cooking liquor.

GEORGE H. TOMLINSON.

RFEREN CES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,253,854 Marchand Jan, 15, 1918 2,285,876 Tomlinson June 9, 1942 2,238,456 Tomlinson Apr. l5, 1941 '757,352 Sanguineti Apr, 12, 1904 2,272,982 Owen Feb. 10, 1942 1,510,196 Romer Sept. 30, 1924 1,218,638 Fest Mar. 13, 1911 OTHER REFERENCES De Becze and Rosenblatt, "Continuous Fermentation, American Brewer, February 1943, pages 1l to 34. Pages 15-34 refer to alcohol.

Certicate of Correction Patent No. 2,429,143.

October 14, 1947.

GEORGE H. TOMLINSON It is hereby and that the said Letters the same may conform to certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column dlsposable read disposal; column l1, line 11, claim 3, after l, line 18, for the word solids insert a comma;

Signed and sealed this 6th day of January, A. D. 1948.

THOMAS F. MURPHY, 

